Hot gas defrosting



Dec. 30, 1947. A. s. NEWTON HOT GAS IVJEFROSTING Filed Apfil so, 1942 m4. (m1: smm/ nan/s mew) INVENTOR.

Alwirp. '8. NQWI'OYLA jig? 4 M ATTORNEY.

Patented Dec. 30, 1947 HOT GAS DEFROSTIN G a Alwin B. Newton, Minneapolis, Minn., asslgnor to Minneapolis-Honeywell. Regulator Company, Minneapolis, Minn., a corporation of Delaware Application April 30, 1942, Serial No. 441,127 (Cl. 62-115) 17 Claims. i

The present invention relates to improved automatic means and arrangements for defrosting the evaporators of refrigerating systems, particularly direct expansion systems.

The primary object of this invention is to pro vide means for accomplishing quick and efiiclent defrosting of an evaporator by admitting hot refrigerant into the evaporator, allowing it to condense therein and then pumping it out.

A more specific object of the invention in connection with the preceding object is to provide a restricted orifice means through which the condensed refrigerant is pumped out of the evaporator, the small size of the orifice causing a slow equalization of the pressures across the orifice for permitting all of the refrigerant to evaporate in the evaporator and not pass over to the compressor as a liquid.

Although this invention may be practiced in systems having but a single evaporator, it finds its widest use in multiple evaporator systems where the evaporators will be defrosted at different times thus assuring that an ample amount of hot refrigerant gas will be available for defrosting purposes.

Another object is to provide a timing mechanism for producing intermittent defrosting cycles, the timing mechanism providing for, in sequence, isolating the evaporator or evaporators to be defrosted and opening a valve admitting hot refrigerant gas to the unit or units to be defrosted, and after the defrosting periods, again in sequence, closing the hot refrigerant valve, opening the restricted orifice means for pumping out the evaporator, and then placing the evaporator or evaporators-back in normal flow relationship with the system. Each evaporator may be provided with such a timing means and the timing means so arranged that not more than a certain percentage of the total number of evaporators could be defrosted at one time.

Numerous other objects and advantages of my invention will become apparent from the following detailed description and annexed drawing, the drawing comprising a single figure which illustrates, more or less diagrammatically, a refrigeration system embodying the various features of my invention.

The invention is directed mainly, although not exclusively, to defrosting of refrigerating units utilized in cold storage plants. Referring to the drawing, numeral 9 designates a, refrigerating unit and controls therefor, forming part of a system which may be employed for refrigerating storage chambers or the like. The unit 9 includes an evaporator I0 forming a part of a direct expansion refrigeration system and a motor drlven'fan ll arranged to circulate air over the evaporator. Other units are indicated at 9a and 9b which also include an evaporator and fan. The evaporators are preferably'withln a duct or a housing through which air is circulated by the fan. The refrigerating system includes a compressor l2 which is driven by an electric motor, the discharge of the compressor being connected to a condenser I3 by a pipe M; The condenser is connected to a liquid receiver I5 by a pipe l6 and the receiver I5 is connected to the evaporators of the units 9, 9a and 922 by pipes l8, l9, 19a and lb. The outlets of the evaporators are connected to the suction side of the compressor by pipes I1, Ila and I'll), these pipes having various branch pipes connected to them which will be referred to presently.

Interposed in the pipe I 9, that is in the liquid line leading to the evaporator-l0, is a. solenoid type stop valve 20 and beyond this valve is a thermostatic expansion valve 2 I of the well known type which maintains a predetermined degree of superheat at the outlet of the evaporator. The valve 2| includes operating mechanism having expansible and contractible chambers one of which is connected to a thermal bulb 22 by means of a capillary tube 23, the thermal bulb being disposed in intimate heat exchange relationship with the pipe connected to the outlet of the evaporator, that is the suction pipe IT. The bulb 22 is filled with-a volatile liquid which vaporizes and develops a pressure depending upon the temperature of the refrigerant gas in the outlet of the evaporator. The other expansible chamber of the operating mechanism of valve 2| is connected by a tube 24 to the outlet pipe 1'! of the evaporator, the tube 24 being known in the art as an external equalizer connection, the pressure in the outlet pipe of the evaporator being utilized as one of the operating forces for the valve 2!. The operation of valves of this type is well known in the art and need not be described in further detail.

Interposed in the suction line I 1 is another solenoid type stop valve 21, it being understood, of course, that the valves 20 and 21 operate between open and closed positions in response to energization and deenergization of an electrical circuit.

Numeral 28 designates a by-pass connection connected to the pipe I! so as to form a by-pass around the valve 21. Interposed in the lay-pass connection is another solenoid stop valve 29 and this valve controls a relatively small orifice through the by-pass 28 when the valve 29 is open.

Numeral 30 designates a pipe forming a connection between the pipe l4 and the suction line providing for a restricted flow of refrigerant or pipe 11. Inter-posed in the pipe 39 is a soleas to be engageable with their respective cams, which, of course, are spaced on the shaft 53. The

member 63 is frictionally mounted on a pivot 61,

or it may be freely mounted'and the switch 62 held in its actuated position due to itsover center type of mounting. With the parts in the position shown the member 63 is rotated in a counterclockwise direction on its pivot so as to cause closure of mercury switch 62, this switch having its electrodes at its left end. When the cams are rotated ina clockwise direction the dwell of cam mands for cooling, and controls are also provided for initiating defrosting cycles at predetermined timed intervals. The purposeof the defrosting cycles, of course, is to remove accumulated frost and ice from the evaporator. Initiation of a defrosting cycle produces particular operation of the system to defrost the evaporator in the most eflicient and expeditious manner as will presently be described.

The defrosting control mechanism includes a time operated switching device 35, this device having a switch arm 36 which may engage either one of two fixedelectrical contacts 31 and 38.

The blade 36 and its two associated contacts control an electric motor 39 through wires 49, 4| and 42, the motor 39 being of a well known type which always operates in the same direction, operating its shaft through 180 whenever the contacts make on one side or the other. 7 Power for operation of the motor 39 is supplied by a step down transformer 43 having a primary winding 44 and a secondary winding 45, the primary winding being connected to line conductors 46 and 41 by wires 48 and 49 respectively. The line conductors 46 and 41 are connected to any suitable source of power not shown It is contemplated that various other types of timers may be substituted, or if desired, a single timer may be substituted for the timer 35 and motor 39.

The motor 39 drives a shaft 53 through a gear train so that the'shaft is rotated at a relatively low speed. Mounted on the shaft '53 are a number of cams which are indicated by the numerals 54, 55, 56, 51, 58 and 59. Each of the cams has a single dwell as shown and with the parts in the position as shown on the drawing the cams are in their initial position as far as operation of the motor 39 is concerned, and with the parts in this position, the dwells are angularly spac with respect to the shaft 53 as shown.

The cam 54 cooperates with a pivoted switch carrying lever 66 carrying mercury switch 6| and with the parts in the positions shown. that is the initial position, the dwell or cam 54 is engaging the lever 69 so as to tilt it in a counterclockwise direction so that the mercury switch is closed, its electrodes being at its left end.

The cams 55 and 56 both operate a single mercury switch 62 mounted-on a switch carryin member 63 having downwardly extending cam follower portions 64 and 65. The cam follower portion 64 is associated with cam 55 and the cam follower portion 65 is associated with the cam shown on the drawing, As actually constructed, of course, the member 63 is arranged substantially at right angles to the shaft 53 and the portions 64 and 65 are slightly offset from each other so 56, the arrangement being as diagrammatically 56 will move away from portion 65 leaving member 83 in the same position, but when the dwell of cam engages portion 64, memben'63 will be rotated in a clockwise direction so as to open mercury switch 62. This will occur after something less than 180" of rotation of shaft 53 in a clockwise direction, and upon continued rotation of shaft 53 the dwell of cam 56 will engage portion so as to tilt member 63 in the opposite direction for closing mercury switch 62.

Numerallll designates another mercury switch mounted on a member ll of the same construction as member 63. Member 'II is mounted on,

a pivot 12 and has downwardly extending cam follower'portlons 13 and I4 cooperable with the cams 51 and 58 which are identical with the cams 55 and 56 respectively, and they operate mercury switch 19 in the same manner .as the mercury switch 62 is operated.

Cam 59 has a single dwell and this cam actuates a pivoted switch carrying lever ll carrying double ended mercury switch I3, that is a mercury switch having electrodes at both ends. With the parts in the position shown, lever fl is tilted in a counter-clockwise direction and the electrodes at the left end of mercury switch 18 are bridged.

The timer 35 is arranged to operate the motor 39 to cause it to operate from an initial position through 180 of rotation of shaft 53 and then back to initial position, these operations occurring at intervals which may be spaced so that they may occur three or four times daily, for example, it, being understood that this will cause defrosting operation of the refrigerating system three or four times during a day. The timer is arranged to cause blade 36 to engage contact 31 at these intervals and when it does so, motor 39 will'opcrate to drive shaft 53 in a clockwise direction through 180. The timer 35 as pointed out above causes blade 36 to engage contact 31 at intervals occurring three or four times daily and the timer is so adjusted that after blade 36 has engaged contact 31, approximately 12 minutes later the blade 36 will engage contact 38. The motor 39, as pointed out above, is of a type which always operates in the same direction, in this instance this being a clockwise direction and the motor 39 is arranged so as to require substantially four minutes to operate the shaft 53 through When blade 36 of the timer has engaged contact 31, motor 39 operates shaft 53 in a clockwise direction as pointed out, and upon this occurring, rotation of cam 54 substantially immediately allows mercury switch 61 to open. After substantially three minutes, the dwell of cam 55 engages portion 64 of member 63 rotating member 63 so as to open mercury switch 62. At the same time mercury switch 16 is opened in the same manner. by cam 51. Substantially at the end of the four minute period required for shaft 53 to turn through 180" the dwell of cam 59 engages lever I! so as to tilt it causing the mercury in mercury switch 18 to move to the other end of the switch bridging the electrodes at the right end and unbridging the electrodes at the left end. The parts will remain in this position for approximately 8 minutes at the expiration of which time blade 85 will have engaged contact 88 so as to reenergize the motor 39 causing the shaft 53 to be rotated another 180 in a clockwise direction, this rotation also requiring substantially 4 minutes. Upon this rotation, substantially immediately, cam 59 will allow the electrodes at the left end of mercury switch 18 to be bridged and the electrodes at the right end to be unbridged. After substantially three minutes of this period of rotation of shaft 53 have elapsed-cam 58 will be in a position to engage portion 14 of member 1| so asto rotate this member in a counter-clockwise direction so as to close mercury switch 10. At the same time cam 58-will cause closure of mercury switch 62. Substantially at the end of this four minute period of rotation cam 54 will cause closure of mercury switch 6|. I v

The timer 35 may be any of various types of interval timers already known in the art and includes a time switch adjustment knob 34.

Any timing device would suflice which would make the contacts on one side three or four times daily with the contacts on the other side being made substantially twelve minutes later in each instance. Momentary closure of the contacts is suflicient inasmuch. as the motor 39 includes maintaining switches and circuits controlled by the motor itself.

During normal operation, the evaporator 10 is controlled by opening and closing the stop valve 20 in the liquid line Hi. This valve is controlled by a thermostat 80 comprising a bi-metal element 8| instance 40.

The motor driving the compressor 12 is conpressure controller 84 which comprises a switch controlling a circuit including a wire 85 leading to the compressor motor, a wire 86 and a wire 81, the wires 85 and 81 being con nected to any suitable source of powernot shown. The suction pressure controller 84 includes an open, this valv being controlled by the electrodes at the left end of.mercury switch 18 which are bridged at this time, the circuit for valve 29 being as follows; from line conductor 41, through wire 93, the left ,30 is closed at this time, this valve being controlled by the electrodes at the right end of mercury compressor in response to a predetermined relatively low pressure in the suction line.

The units 9a and 9b are each provided with controls which may be duplicates of the controls described above for the unit 9. The timers are shown, the

of conduits 30a and 30b respectively.

switch 18.

The solenoid valve 20 in the liquid line as pointed out, is controlled by mercury switch (ii and thermostat and with the parts in the position shown mercury switch BI is closed and the contacts of thermostat 80 are made indicating a demand for refrigeration so the valve. 20 is energized through the following circuit: from line conductor 41 through wire 91, mercury switch 6!, wire 98, contact 83, blade 82,,element 8|, wire 99, valve 20 and wire I80 back to line conductor 46. Valve 20 being open, liquid refrigerant is admitted to the evaporator from condenser l3 and receiver operate. The fan II is in operation for circulating air over the evaporator Of unit It), the operation of fan i'l being controlled by mercury switch 62 and its circuit being through wire IIH, mercury switch 62, wire I02, the motor of and wire 103 back to line conductor 46.

The system will operate under these circumstances to maintain a predetermined temperature in the refrigerated compartment, the controller 84 acting to stop the compressor whenever the suction pressure is reduced to a predetermined value.

When the timer 35'causes blade 38 to engage contact 31 at one motor 39 has operated for substantially 3 minutes, for example, cams 55 and 51 will open mercury thus stopping the 28 and opening 30. With thevalves 29 closed the evaporator is isolated from the system as far as the normal circulation of refrigerant is concerned. With the valve 3| open, hot gas from the condenser is permitted to g the beginning of this 4 elapsed, cams described above. This stat 80 and if there is a demand for the compressor in the'form of flow freely into the evaporator through pipe 30 and pipe IL This hot gas upon entering the evaporator will condense, thereby giving upa considerable amount of heat which will serve to defrost the evaporator. The defrosting action will be allowed to continue for substantially an 8 minute period,the motor 39 as pointed out above remaining in its position wherein the mercury switches are open for a period of substantially 8 minutes. At the end of this period, blade 36 of the timer will engage contact 38 reenergizing the motor 39 causing it to again of substantially 4 minutes, the motor again operating in a clockwise'direction. Substantially at minute period cam 59 will operate mercury switch 18 to the position shown on the drawing, wherein the circuit of valve Si is interrupted for closing this valve and the circuit of valve 29 is reenergized for opening this valve. Valve 21 will remain closed for a period of perhaps 3 or 3 /2 minuteswhile valve 29 is open and shaft 53 is rotating. Opening-of valve 29 will, of course, permit refrigerant to pass through its restricted orifice to provide for the gradual decrease in pressure in the evaporator which will give practically all of the condensed refrigerant time enough to evaporate and pass through the valve 29 as a gas. This being an upfeed evaporator it may be desirable to provide a restricted bypass. llliand check valve I06 around the valve 20 and expansion valve 2| to provide any liquid refrigerant which may accumulate in the bottom of .the coil an opportunity to pass into'the hi h side of the line IS. The pressure in pipe is will be slightly lower than that in the evaporator when valve is closed and valve 3| open. The purpose, therefore, of the valve 29 with its small orifice is to prevent any liquid refrigerant from entering the compressor after the evaporator has been defrosted.

After substantially p e.

3 or 3%minutes, .for exam- 55 and 58 will cause closure of mercury switch 62 and respectively in the manner will cause restarting of the fan II and. reopening of the stop valve 21 in the suction line. Substantially at the end of the 4 minute period, cam 54 will reclose mercury switch 8| putting valve 20 back under control of thermoa refrigeraoperate for a period 1. In apparatus of thecharacter described, in combination, means forming a refrigerating system including an evaporator and a source of refrigerant supply normally connected in refrigerant fiow relationship, said source being capable of supplying hot refrigerant, defrosting apparatus comprising means for closing the liquid and suction lines of the evaporator, means for communieating l'iot gas from the said source directly to the evaporator so that said gas may condense in the evaporator for defrosting it, and means forming a relatively restricted orifice connecting said source and evaporator by which refrigerant used for defrosting is withdrawn from the evaprator and returned to the inlet of said said source, the restricted orifice acting to prevent refrigerant in liquid form from returning to said inlet.

2. In apparatus of the character described, in

combination, means forming a. refrigerating sysof the last mentioned 4 minute period have tion at the time valve 20 will be opened and the 5 system will again operate normally.

As set forth above, the other two units to and be successfully employed in a system having one unit. Those skilled in the artwill appreciate from the foregoing that the system herein disclosed provides an eflicientand expeditious method of defrosting an evaporator whereinthe defrosting operation is so arranged and sequenced that the refrigerant used for defrosting is not returned to liquid.

The form of my invention, which I have disclosed, is representative and it will be understood that various modifications and changes will oc- ;cur to those skilled in the art. The disclosure is illustrative and the invention is to be limited only in accordance with the'claim's appended hereto.

I claim as my invention:

time. A total of three units are disclosed herein but it will be read ily'appreciated that my invention is applicable to a system employing any number of units, and may Sb are defrosted in the same manner but the l tem omprising a refrigerant evaporator and a source of refrigerant normally connected in refrigerant flow relationship, said source being capable of supplying hot refrigerant, means for isolating said evaporator as far as said .normal flow relationship is concerned, means by which hot refrigerant from said source is communicated tosaid evaporator for defrosting it, said refrigerant being returned to the source when the evaporator is again placed in normal refrigerant fiow relationship with the source of refrigerant, and automatic defrosting control means for operating said isolating means and communicating means upon a demand for defrosting and for causing said communicating means to cut off the fiow of hot refrigerant after defrosting.-

3. In apparatus of the character described, in combination, means forming a refrigerating system comprising a refrigerant evaporator and a source of refrigerant normally connected in refrigerant flow relationship, said source being capable of supplying hot refrigerant, means for isolating said evaporator as far as said normal flow relationship is concerned, means by which but refrigerant from said source is communicated to said evaporator for defrosting it, means having a. relatively restricted orifice through which refrigerant used for defrosting is returned to the inlet of the source, the restricted orifice acting to prevent refrigerant in liquid form from returning to said inlet; and automatic defrosting control means for operating said isolating means and communicating means upon adamand for defrosting and for causing said communicating means to cut off the flow of hot refrigerant after frigerant flow relationship, said source being capable of supplyinghot refrigerant, means for isolating said evaporator as far as said normal flow relationship is concerned, means by which hot refrigerant from said source is communicated to said evaporator for defrosting it, means having a relatively restricted orifice through which refrigerant used for defrosting is returned to the inlet of the source, the restricted orifice acting to prevent refrigerant in liquid form from returning to said inlet, and automatic defrosting control means comprising timing means for sequentially operating the isolating means and communicating demand for defrosting and for causing the communicating means to cut off the flow of hot refrigerant after defrosting before the refrigerant used for defrosting is returned to the source through said restricted orifice means.

5. In apparatus of the character described, in combination, a refrigerating system including a compressor, condenser and expander connected in refrigerant flow relationship. valve means for closing the liquid and suction lines of the expander, means ,for conveying hot refrigerant to the expander when said valve means are in closed position, and means having a relatively restricted orifice connecting said expander and the suction side of said compressor through which refrigerant may be withdrawn from the expander by said compressor when said valve means are in closed position.

6. In apparatus of the character described, in

combination, a refrigerating system including a compressor, condenser and expander connected in refrigerant flow relationship, valve means for closing the liquid and suction lines of the expander, connections for conveying hot refrigerant to the expander when said valve means are in closed position, and a, passage having a, valve means associated with a relatively restricted orifice connecting said expander and the suction side of the compressor through which refrigerant may be withdrawn from the expander when said valve means are in closed position, said valve means including a stop valve in the suction line and said passage having a valve means associated with a restricted orifice being arranged in by-pass relationship with said stop valve in the suction line.

7. A refrigeration system comprising'in combination, refrigerant compressor means, a plurallty of evaporators, means for condensing the compressed refrigerant, means conducting condensed refrigerant from said condensing means to theinlet of each of said evaporators, means connecting the outlet of each-of said evaporators to the suction side of said compressor means, and means for defrosting at least one of said evaporators, said last named means including means for preventing the flow of condensed refrigerant to the inlet of said evaporator, means conducting hot compressed refrigerant gas to said evaporator for heating the same and means adjustable to prevent all of said evaporators from being defrosted at the same time whereby hot refrigerant gas will be available for defrosting purposes whenever said compressor is operating.

8. The method of defrosting a refrigerating system of the type including a compressor, a condenser andan evaporator, comprising, closing ofi communication between the inlet of the evaporator and the condenser and between the outlet of the evaporator and the suction side of said compressor and supplying hot gaseous refrigerant to the evaporator through its outlet directly from the compressor until the evaporator is defrosted, then discontinuing the supply of hot gaseous refrigerant to the evaporator and connecting said evaporator to the suction side of the compressor through a restriction to gradually remove the refrigerant in the evaporator, and finally establishing normal communication between the inlet of the evaporator and the condenser and between the outletof the evaporator and the suction side of the compressor.

9. The'method of defrosting a refrigerating system of the type including a compressor, a condenser and an evaporator; comprising, first closing ofi communication between said condenser outlet of the evaporator to the suction side of the compressor through a restriction to gradually remove the refrigerant in the evaporator, and finally establishing normal communication between the inlet of the evaporator and the condenser and between the outlet of the evaporator and the suction side of the compressor.

10. A defrosting arrangement for a refrigeration system of the usual compressor, condenser, and evaporator type, comprising, in combination, liquid line valve means operable to establish-or close oil communication between the condenser and the inlet of the evaporator, suction line valve means operable to establish or disrupt sequence means in control of said valve means to first operate said liquid line valve means to prevent communication between said condenser and evaporator and thereafter to' operate said suction line valve means and said gaseous refrigerant valve means to prevent communication between said evaporator and the suction side of said compressor and to establish communication between the outlet. Of said compressor and said evaporator to supply hot gaseous refrigerant to said evaporator to defrost the same and then to close said gaseous'refrigerant valve and to open the valve means in said by-pass.

11. A defrosting arrangement for a refrigeration system of the usual compressor, condenser, and evaporator type, comprising, in combination, liquid line valve means operable to establish or close off communication between the condenser and the inlet of the evaporator, suction line valve means selectively operable to establish full or restricted communication or to disrupt fully orator and the suction side of said communication between the outlet of said evapcompressor, gaseous refrigerant valve means operable to establish or close off communication between the outlet of said compressor and said evaporator, and sequence means in control of said valve means operable first to operate all of said valve means to close off communication from the evaporator to the condenser and suction side of the compressor and to establish communication between the outlet of the compressor and the evaporator, to thereafter operate said gaseous refrigerant valve means to close off communication between the outlet of the compressor and the evaporator and to establish restricted communication between the outlet of the evaporator and the suction side of the compressor, and to finally reestablish full communication from the condenser to the evaporator and thence to the suction side of the compressor.

12. A defrosting arrangement for a refrigeration system of the usual compressor, conde and evaporator type, comprising, in combination,

11' liquid line valve means operable to establish or close of! communication between the condenser and the inlet of the evaporator, suction line valve means selectively operable to establish full -or restricted communication or to disrupt fully communication between the outlet of said evaporator and the suction side of saidcompressor, gaseous refrigerant valve means operable toestablish or close off communication between the outlet of said compressor and said evaporator, and sequence means in control of said valve means operable to first operate said liquid line valve means I to prevent communication between said condenser and evaporator, to thereafter operafi said suction line valve means and said gaseous refrigerant valve means to prevent communication between said between the outlet of said compressor and said evaporator, to then operate said gaseous refrigsaid normal flow relationship'is concerned, means I for introducing hot refrigerant from said source to the isolated evaporator for defrosting it, and means having a relatively restricted orifice connecting the evaporator to'said source through which refrigerant used for defrosting is returned directly to the inlet of'the source only after the introduction of hot refrigerant to said evaporatorhas ceased, the restricted orifice acting to 10, prevent refrigerant in liquid formfrom returning 15 source of refrigerant normally connected in reevaporator and the suction side of saidcompressor and to establish communication l i u erant valve means to close off communication between the outlet of the compressor and the evaporator and to establish restricted communication between theoutlet of the evaporator and the suction side of the compressonand finally to reestablish fullcommunication from the condenser to the evaporator and thence to the suction side of the compressor. h

13. In apparatus of the characterdescribed, in combination, vmeans forming a refrigerating system including an evaporator and a source of refrigerant supply normally connected in refrigerant flow relationship, of supplying hot refrigerant, cyclically operated means for closing the liquid and suction lines of the evaporator to stop said normal refrigerant flow relationship, and means for supplying hot gas from the said source directly to the evapo-' rator while said normal refrigerant flow is stopped so that said gas may condense in the evaporator for defrosting it. a

14. In a refrigerating system, in combination,

said source being capable.

frigerant flow relationship, said source being capable of supplying hot refrigerant and having an inlet, means for isolating said evaporator from said normal flow relationship including a valve for controlling flow between said evaporator and said inlet, means by which hot refrigerant from said source is communicated to said evaporator for defrosting it, and conduit means including a fluid flow restriction connected in by-pass rela tion to said valve through which refrigerant used for defrosting may be returned to said source.

17. In apparatus of the character described, in

combination, means forming a refrigerating system comprising a refrigerant evaporator and a 0; source of refrigerant normally connected in refrigerant flow relationship, said source being capable of supplying hot refrigerant and having an inlet, means for isolating said evaporator from said normal flow relationship including a 5 suction valve for controlling flow between said evaporator and said inlet, means, by which hot refrigerant from said source is communicated to said evaporator for defrosting it, and conduit means including a fluid flow restriction and valve 40 means connected in by-pass relation to said sucan evaporator, a source of refrigerant, said source being capable of supplying hot refrigerant, means connecting said evaporator and said source in normal refrigerant flow relationship, means for preventing normal refrigerant flow through said evaporator, means for supplying hot refrigerant from said source directly to said evaporator for defrosting the same, and means including a restriction for returning refrigerant used for defrosting'to said source. a

' 15. In apparatus of the character described, in combination, means forming a refrigerating system comprising a refrigerant evaporator and a source of refrigerant normally connected in refrigerant flow relationship, said source being cae pable of supplying hot refrigerant, means for positively isolating 'said evaporator as far as Number Name Date 1,912,841 Haymond June 6, 1933 2,049,413 Cannon Aug. 4, 1936 2,069,201 Allison Feb. 2, i937 2,110,693 Bailey Mar. 8, 1938 2,128,386 Warren Aug. 30, 1938 FOREIGN PATENTS Number Country Date tion valve through which refrigerant used for defrosting may be returned to the said source.

ALWIN n. NEWTON. REFERENCES CITED The followingreferences are of record'in the file of this patent:

' UNITED ST TES PATENTS Germany Dec. 4, 1888 of the character described, in. 

